The 1968 Hallicrafters WR-600 (S-120) is nearly ready for use in CW QSOs after realizing Dave Cripe’s (NM0S) filter will provide the needed additional filtering. This video contains a sampling of Monday morning’s CW chatter on 40m. As the video shows, the filter has awesome performance; forget the fact this is a four-tube shortwave receiver built in 1968!
According to the filter assembly manual, it uses "four, two-pole Sallen-Key opamp filters; three low-pass filters, and one high pass filter. Each filter section is fairly low-Q, and the frequencies of resonance are staggered. Cascading these four sections in series creates the optimal filter response." The filter circuit is based on the Dave's May, 1994 article in '73' magazine. The filter kit is still listed for sale at less than $30 on 4sqrp website. The Four States QRP website has link to the magazine article, well worth reading.
The external Beat Frequency Oscillator (BFO) 455 KHz is a Ten-Tec kit module board kit model 1050, no longer in production. Antenna is half wavelength dipole inverted-V fed with homemade twisted-pair transmission line, and the feed point height is 26 feet (8 meters) above ground surface.
My next step is to use the Hallicrafters receiver in a CW QSO!
73 NG9D
12 сен 2024
